The present invention relates to a method according to the preamble of claim 1 and a device according to the preamble of claim 4. Methods of mounting electric components on wiring boards or printed circuit boards are known.
Generally, electric components of any desired type can be fastened on wiring boards or printed circuit boards or other large-area supports by positioning them on the circuit board, together with their housing, and by providing the housing for example with mounting flanges through which fixing means, such as screws or the like, can be passed for screwing the elements in place on the circuit board. Another known method consists in positioning the electric components directly on the circuit board and passing the connection wire ends through bores in the circuit board and soldering them on the opposite face thereof. This method is frequently used for resistors, transistors, or the like because in these cases the connection wires are sufficiently strong to carry the mass of such a component safely and to secure it against vibration.
Larger components require, however, separate mounting means which may for example be designed in such a manner that the housings accommodating or carrying such components are provided with detent legs which exhibit pronounced nose-shaped projections. The legs are passed through corresponding openings in the circuit board to engage the circuit board from the bottom so that the components are clamped and fixed in place in a form-locking manner. However, problems are encountered with such components which are clipped and clamped in place by means of locking noses coacting with recesses in the carrier plate. In particular, when the components in question are big and heavy, as in the case of transformers, capacitors, relays, anti-interference coils, or the like, and when the printed circuit boards on the other hand are subjected, during operation of the equipment in which they are installed, to vibration, movements or oscillation, the detent legs, which retain the components in position only by their initial stress may upon corresponding transverse acceleration, come out of the openings of the printed circuit board.
It has, therefore, been proposed in connection with the known mounting means for electric components to provide fixing legs adjacent the detent legs exhibiting the locking noses. This forms an additional contact face for the opening in the carrier plate so that, after engagement of the locking noses, the free space required for permitting the locking noses to give way and engage the board is taken up and the whole locking means come to rest flush against the walls of the openings in the carrier boards.
This may, however, lead to a quite considerable increase in complexity of the shape of the housings carrying the components, in the area of the mounting and locking means. In addition, a certain distance has to be maintained between the detent leg and the related fixing leg to permit the initial deflection of the detent leg which is required to permit the locking nose to pass through the opening in the circuit board which is then engaged by it.
Reverting once more to the locking arrangement using simple detent legs, which in the case of a component of circular cross-section may, for example, be set off relative to each other by 90.degree. or 120.degree., with the locking noses pointing outwardly, the cross-section of the opening in the printed circuit board must at least be large enough to permit the head of the respective detent leg, which carries the locking nose, to pass if the respective detent leg with the locking nose extending vertically to the direction of introduction, i.e. in the transverse direction, is to be introduced. After engagement of the bottom surface of the circuit board, one necessarily always obtains a gap corresponding to the projection formed by the locking nose in the transverse direction; otherwise it would not be possible to pass the respective detent leg through the corresponding receiving opening. For the usual mounting method by means of detent legs this means that the component is always held loosely in its mounting hole, and this possibly also when, as mentioned before, several such detent legs with locking noses pointing in different directions are provided. Even if the detent legs are biased appropriately to be urged outwardly into contact with the wall of the opening after engagement of the board, greater acceleration effects acting in the transverse direction may cause the component to tilt and to be jammed in the receiving openings, due to the still existing tolerances, so that under certain circumstances one or more of the detent legs may come off their engaged position. Accordingly, an acceleration effect acting in a different direction may cause all the detent legs to come free. The respective electric component, for example a transformer which is always relatively heavy due to its content of heavy iron, or an anti-interference coil, or a capacitor, are then detached from the carrier plate which leads not only to considerable damage, but in any case also to destruction of the corresponding electric functions of the unit.
Further, it is not possible in the case of the known means for mounting electric components on printed circuit boards, to realize or, at least, to prepare the electric connection simultaneously with a mounting process of this type. For example, if transformers, anti-interference coils or capacitors have to be arranged, it is necessary to connect soldering pins with the normally relatively thin connection wires of the windings of a transformer or of a coil. These pins are then seated in suitable recesses of the housing extending towards the circuit boards a length sufficient to ensure that during mounting of the housing, the soldering pins can be passed through suitable bores in the circuit board to enable them to be soldered on the reverse side, i.e. on the conductor side of the circuit board. Although it is sometimes possible to do without such separate soldering pins, namely when the connection wires are relatively thick, it is still necessary in this case to thread the wires carefully through the associated holes, or at least to bring them into proper alignment with the latter. Still, during assembly, it happens rather often that when the detent legs are pressed home the respective electric connection pin, i.e. soldering pin or connection wire, gets tilted in its opening, is dislodged upwardly, comes off its seat, and may even be torn off.
All these disadvantages can be overcome only with great difficulty and considerable cost and cause particularly severe problems where the respective electric component to be mounted on the base plate is relatively heavy itself, so that it cannot be retained by its own electric connection lines, as is the case, for example, with the before-mentioned coils, capacitors, relays, anti-interference coils, or the like.
Now, it is the object of the present invention to provide a method and a device for seating or mounting electric components on a wiring board or printed circuit board in which on the one hand the known method of mounting the housing which carries or receives the electric component by means of detent legs is maintained while, on the other hand, it is ensured that the detent legs cannot by any means come off their engaged position. Also it is ensured by the same means that the corresponding connection wires of the electric component will thread into the associated openings of the printed circuit board practically automatically and in safe alignment. The present invention provides the possibility to achieve simultaneously both objectives, i.e. safe locking and unproblematic threading-in of the connection wire.